Writing a literary commentary is not as difficult as it first seems.
As with any new skill it needs practising even to those who take to it naturally. Think of the last time you had to try something new such as learn a new swimming stroke, or how to ice-skate, or make chicken fried rice... they all require patience and practice.

As a Standard Level student, you will have an hour and a half to read, annotate, organise and write a literary comment based on an extract of text that could be taken from a novel, an essay, a biography, a piece of journalism or drama.
http://www.ehow.com/how_4897392_write-poem-commentary.html

http://www.wikihow.com/Write-a-Literary-Commentary


Another way is to apply the Who What Where When Why and How questions.
For SL, Paper 1 is known as the Guided Literary Analysis. You will be given two questions which will almost always be:
1. concerning Content -- this will generally be about the setting, characters, action and ideas or the sub-text
2. concerning Style -- you need to say something about form, the effects of language choice and syntax/ sentence structure -- aesthetics, mainly.

Here is take-away handout if you think you need one